In the past, the method has been known of crushing a stock pulp sheet by a crusher to produce crushed pulp, forming component parts such as a nonwoven fabric or absorbent mat from the produced crushed pulp, and assembling these component parts to produce a product such as a disposable diaper or sanitary napkin.
In this regard, a stock pulp sheet sometimes includes a defective part where for example a piece of bark or other foreign matter is mixed in or changes color. If such a defective part for example remains at the surface in contact with the skin such as the top sheet, the commercial value of the product will end up falling.
Therefore, a defective product rejection system which detects a defective part present in a product and rejects a product containing the defective part as a defective product is known (see PLT 1).